A concern when using an electrical appliance, such as an appliance having a heating element, is leaving the appliance unattended while it is operating. As such, it has been known to provide some appliances with an automatic shut-off feature that activates after some predetermined period of time of non-use of the appliance.
For example, commonly assigned U.S. Pat. No. 4,745,260, entitled "Automatic Switching Apparatus for an Electrical Appliance", by H. Albinger, Jr. et al., provides a motion sensor and an electronic timer to automatically shut off a pressing iron if the iron remains stationary for a predetermined period of time.
Also by example, commonly assigned U.S. Pat. No. 4,727,240, entitled "Electric Iron with Dual Automatic Cutoff", by D. J. Provolo et al., discloses an electric iron that employs two timing cycles for turning off power to the iron upon the absence of motion for two different discrete time periods. A motion sensor includes an attitude sensor to enable a short timing cycle for cutting off power after the electric iron is motionless with its sole plate in a substantially horizontal orientation. A longer timing cycle is enabled when the electric iron is motionless with its sole plate oriented in other than the horizontal detection range.
Both of the above referenced commonly assigned patents employ a mechanical or electromechanical apparatus to sense motion or lack of motion of the pressing iron.
Commonly assigned U.S. Pat. No. 4,743,736, entitled "Switching Apparatus for an Appliance Control Circuit", by H. Albinger, Jr. et al. discloses a switching apparatus useful with an electric iron control circuit. The control circuit is responsive to a movable contact member to generate a series of pulses for use by a microcomputer of an appliance control circuit to operate audible and visual status indicators.
The following U.S. Patents are cited for showing various types of switching arrangements for an electrical appliance.
U.S. Pat. No. 4,203,101, entitled "Electric Power Interrupting Apparatus" by Towsend, discloses a sensor controlled electric power interrupter for a pressing iron. A touch sensor senses hand skin contact and is attached to the handle of the iron. The sensor is a capacitance-controlled switching circuit that changes state when the capacitance of the body of the operator is connected to the circuit by the operator's hand skin contact. The sensor is used in conjunction with an orientation sensor (horizontal or vertical). In some embodiments a timer is employed, in conjunction with the orientation sensor, to shut off power to the iron after a predetermined period.
U.S. Pat. No. 4,520,257, entitled "Electronic Non-Use Power Interruption Safety Device for an Electric Flat-Iron" by Schwob et al., discloses a movable body contained within the housing of the iron for interrupting power at the end of a predetermined interval of non-use.
U.S. Pat. No. 4,130,955, entitled "Pressing or Smoothing Iron Comprising a Safety Turn-Off Means Located in a Heating Current Circuit" by Baumgartner et al., discloses the use of an acceleration sensor comprised of a ball located in a curved channel within the body of an iron. When the pressing iron is left lying motionless on the goods being ironed, disconnection of electric power occurs after a predetermined period of time.
U.S. Pat. No. 4,859,869, entitled "Safety Switching Means for Controlling a Current Consumer" by Heuwinkel et al., discloses the use of an optical transmitter and receiver to detect the presence of the user's hand upon the handle of a pressing iron. A position-responsive sensing device (mercury switch) is employed with the optical sensor such that, when the iron is in a horizontal working position, the heater current is influenced only by the optical sensor.
U.S. Pat. No. 4,686,352, entitled "Electronic Pressing Iron" by Nawrot et al., discloses an electric pressing iron that includes a motion and attitude sensor that is connected to a timer to disable the electric heater of the iron depending on iron orientation and movement.
U.S. Pat. No. 4,692,589, entitled "Electric Iron Having Safety Cutoff Switch and Temperature Indicator" by Borsari et al., discloses an electric iron having an orientation-detecting switch and a timing circuit which, after the iron is unmoved in the horizontal or vertical position for preset times, triggers a manually resettable thermostatic cutoff switch.
U.S. Pat. No. 4,803,342, entitled "Flat-Iron Safety Device Utilizing a Dual Internal Timing Circuit" by Steers et al., discloses the use of a pivotally mounted magnet for sensing orientation of the iron. A dual interval timing circuit provides first and second timing intervals for interrupting electric current to the iron.
In general, the above referenced patents require the use of a mechanical-type orientation or motion sensor, or require a combination of sensors, such as an optical sensor with an orientation sensor, to provide power control in an electrical appliance. As can be appreciated, sensors that employ a moving element are subject to failure. Furthermore, when constructing consumer appliances, a desirable goal is to reduce both cost and complexity. As such, the use of a plurality of sensors can result in higher cost and complexity.
The following two U.S. Patents are cited for showing switching circuits.
U.S. Pat. No. 4,641,132, entitled "Condition-Responsive Switching Circuit" by Reger discloses the diversion of power when a detecting circuit senses a change in a condition being monitored.
U.S. Pat. No. 4,168,443, entitled "Two-Wire Proximity Detector" by Periot discloses a proximity sensor that includes a probe having an output that is sensed by circuitry for triggering a thyristor.